1. Field of Invention
The present invention relates to a power control circuit, and more particularly to a power control circuit applied to a display device for reducing power consumption.
2. Related Art
A new energy code has been executed in the European Communities, in which the no load power consumption of a power supply must be lower than some restriction, and the restriction has become stricter. Besides, in the United States, President George W. Bush has subscribed an executive order, stating that all federal government units must purchase electronic/electrical appliances consuming less than 1 W of power in the standby state.
For conventional power control circuits, if a mechanical switch is not employed as the basic element, generally, the function of peripheral circuits is controlled for sustaining the operation of the system IC, thereby achieving power on and off. Therefore, at least a basic power is required for operation of the IC system. Even if a device is powered off by the switch, in fact the device is still in operation. As a result, power consumption cannot be reduced.
For example, Taiwan Patent No. 561334 discloses a Power Management System of a liquid crystal display (LCD), wherein an LCD device enters a normal mode or a power-saving mode respectively according to the enabling state or the disabling state of a synchronous signal. The disclosed power management system includes a power supply device, an electric power input switch device and a detection device. The power supply device converts a line voltage of an electric power source to supply it to the aforementioned display device. When the electric power input switch device is on, the line voltage is supplied to the power supply device, while when the electric power input switch device is off, the line voltage stops being supplied to the power supply device. The detection device is used to detect the synchronous signal switched from an enabling state into a disabling state, and then turn off the above-mentioned electric power input switch device after a predetermined time period.
To reduce power consumption, a method adopts, for example, a trigger mode in the standby state, in order to meet the regulation issued by the International Energy Agency (EA), i.e., the power consumption in the standby state should be lower than 1 W. The standard regulation prescribes the amount of standby power consumed by the switch mode power supply (SMPS) when the system is in a standby state.
As energy standards become stricter, the standby power consumption is required to be lower than 1 W, which is not easy for the power consumption of present electronic parts and devices. However, in order to meet the stricter power-saving standards, it has become a desired technical demand to reduce the power consumption of electronic devices in the standby state.